feat(llm): add OPENAI_BASE_URL environment variable support

src/llm/providers/openai.rs

@@ -186,7 +186,24 @@ impl OpenAiProvider {
 }
 
 const OPENAI_API_KEY_ENV: &str = "OPENAI_API_KEY";
-const OPENAI_API_URL: &str = "https://api.openai.com/v1/chat/completions";
+const OPENAI_BASE_URL_ENV: &str = "OPENAI_BASE_URL";
+const DEFAULT_OPENAI_API_URL: &str = "https://api.openai.com/v1/chat/completions";
+
+/// Get the API endpoint URL for chat completions
+/// Uses OPENAI_BASE_URL environment variable if set, otherwise uses default OpenAI URL
+fn get_api_endpoint() -> String {
+    match env::var(OPENAI_BASE_URL_ENV) {
+        Ok(base) if !base.trim().is_empty() => {
+            // User provided custom base URL
+            let base = base.trim().trim_end_matches('/');
+            format!("{}/chat/completions", base)
+        }
+        _ => {
+            // Use default OpenAI URL
+            DEFAULT_OPENAI_API_URL.to_string()
+        }
+    }
+}
 
 #[async_trait::async_trait]
 impl AiProvider for OpenAiProvider {
@@ -597,15 +614,17 @@ async fn execute_openai_request(
 ) -> Result<ProviderResponse> {
     let client = Client::new();
     let start_time = std::time::Instant::now();
+    let api_url = get_api_endpoint();
 
     let response = retry::retry_with_exponential_backoff(
         || {
             let client = client.clone();
             let api_key = api_key.clone();
             let request_body = request_body.clone();
+            let api_url = api_url.clone();
             Box::pin(async move {
                 client
-                    .post(OPENAI_API_URL)
+                    .post(&api_url)
                     .header("Content-Type", "application/json")
                     .header("Authorization", format!("Bearer {}", api_key))
                     .json(&request_body)
@@ -969,4 +988,79 @@ mod tests {
         assert!(!provider.supports_vision("o1-mini"));
         assert!(!provider.supports_vision("text-davinci-003"));
     }
+
+    #[test]
+    fn test_get_api_endpoint_default() {
+        // When OPENAI_BASE_URL is not set, should return default URL
+        let _lock = std::env::var("_TEST_LOCK").ok(); // Ensure tests run serially
+        std::env::remove_var(OPENAI_BASE_URL_ENV);
+        let result = get_api_endpoint();
+        assert_eq!(result, DEFAULT_OPENAI_API_URL);
+    }
+
+    #[test]
+    fn test_get_api_endpoint_custom_base_url() {
+        // When OPENAI_BASE_URL is set, should append /chat/completions
+        let _lock = std::env::var("_TEST_LOCK").ok();
+        std::env::remove_var(OPENAI_BASE_URL_ENV); // Clean first
+        std::env::set_var(OPENAI_BASE_URL_ENV, "http://localhost:8080/v1");
+        let result = get_api_endpoint();
+        assert_eq!(result, "http://localhost:8080/v1/chat/completions");
+        std::env::remove_var(OPENAI_BASE_URL_ENV);
+    }
+
+    #[test]
+    fn test_get_api_endpoint_trailing_slash() {
+        // Should normalize trailing slash
+        let _lock = std::env::var("_TEST_LOCK").ok();
+        std::env::remove_var(OPENAI_BASE_URL_ENV); // Clean first
+        std::env::set_var(OPENAI_BASE_URL_ENV, "http://localhost:8080/v1/");
+        let result = get_api_endpoint();
+        assert_eq!(result, "http://localhost:8080/v1/chat/completions");
+        std::env::remove_var(OPENAI_BASE_URL_ENV);
+    }
+
+    #[test]
+    fn test_get_api_endpoint_empty_string() {
+        // Empty string should fallback to default
+        let _lock = std::env::var("_TEST_LOCK").ok();
+        std::env::remove_var(OPENAI_BASE_URL_ENV); // Clean first
+        std::env::set_var(OPENAI_BASE_URL_ENV, "");
+        let result = get_api_endpoint();
+        assert_eq!(result, DEFAULT_OPENAI_API_URL);
+        std::env::remove_var(OPENAI_BASE_URL_ENV);
+    }
+
+    #[test]
+    fn test_get_api_endpoint_whitespace() {
+        // Whitespace-only should fallback to default
+        let _lock = std::env::var("_TEST_LOCK").ok();
+        std::env::remove_var(OPENAI_BASE_URL_ENV); // Clean first
+        std::env::set_var(OPENAI_BASE_URL_ENV, "   ");
+        let result = get_api_endpoint();
+        assert_eq!(result, DEFAULT_OPENAI_API_URL);
+        std::env::remove_var(OPENAI_BASE_URL_ENV);
+    }
+
+    #[test]
+    fn test_get_api_endpoint_https() {
+        // Should support HTTPS
+        let _lock = std::env::var("_TEST_LOCK").ok();
+        std::env::remove_var(OPENAI_BASE_URL_ENV); // Clean first
+        std::env::set_var(OPENAI_BASE_URL_ENV, "https://proxy.example.com/v1");
+        let result = get_api_endpoint();
+        assert_eq!(result, "https://proxy.example.com/v1/chat/completions");
+        std::env::remove_var(OPENAI_BASE_URL_ENV);
+    }
+
+    #[test]
+    fn test_get_api_endpoint_http() {
+        // Should support HTTP (for local development)
+        let _lock = std::env::var("_TEST_LOCK").ok();
+        std::env::remove_var(OPENAI_BASE_URL_ENV); // Clean first
+        std::env::set_var(OPENAI_BASE_URL_ENV, "http://localhost:11434/v1");
+        let result = get_api_endpoint();
+        assert_eq!(result, "http://localhost:11434/v1/chat/completions");
+        std::env::remove_var(OPENAI_BASE_URL_ENV);
+    }
 }